This invention relates to a focused ion beam irradiating apparatus, and more particularly to a technology for adjusting an electron shower in a focused ion beam system having a function to irradiate an electron shower for the purpose of preventing a sample surface from being charged.
As a system for carrying out correction of a pattern formed on a surface of a sample such as a photomask or reticle, etc., a focused ion beam irradiating apparatus is widely used. Generally, when an ion beam is irradiated onto such a sample, the sample surface is charged by positive charges of ion. However, when any charged or electrified state takes place on the sample surface, there would occur the drawback that the sample surface cannot be observed, etc. For this reason, a method of neutralizing positive charges of ion by electron is adopted. Namely, an electron gun for irradiating an electron shower for neutralization is prepared separately from an ion gun for irradiating an ion beam, thus to carry out irradiation of an electron shower together with irradiation of an ion beam.
However, in order to suitably carry out neutralization for positive charges of ion, it is required to adjust an irradiation current quantity, or an irradiation position range, etc. of an electron shower. As such an adjustment method, there is, e.g., disclosed in the Japanese Patent Laid Open Application No. 76662/89 publication, a method in which a conductive sample surface and a non conductive sample surface are prepared to adjust an electron shower so that both images obtained at the time of irradiation of an ion beam are equivalent to each other. With this method, however, there is the problem that since it is impossible to quantitatively recognize the irradiation state of an electron shower, sufficient adjustment cannot be carried out. As a method of obtaining quantitative information, there are carried out a method of irradiating an electron shower on a fluorescent sample to observe the state of the irradiated shower, and a method of irradiating an electron shower onto a substrate on which a resist is coated, etc. thereafter to develop this resist to observe that image. Even with these methods, however, there are the problems that correct information cannot be obtained, and that it takes much time for implementation thereof.